1. Field of the Invention
This invention relates to techniques for producing carbon-containing steel shapes, directly from prereduced iron ore pellets, utilizing the electroslag melting process.
2. Description of the Prior Art
The electroslag process is a secondary melting technique developed some 30 years ago. It conventionally utilizes a consumable electrode of the metal or alloy to be melted. At the beginning of a typical melt, an arc is struck between the electrode and a base plate placed in the bottom of a water-cooled copper crucible containing a fluxing agent. The arc is immediately quenched by fusing flux. After fusion of the flux is complete, power applied to the electrodes is increased and the consumable electrode begins melting. Droplets of metal fall through the flux, collect in a pool on the base plate, and begin to solidify. As solidification proceeds, an ingot forms on the base plate and grows upwardly with a molten pool of metal on top. Molten flux in contact with the water-cooled crucible solidifies during the melt to form a thin skin between the crucible and the solidifying ingot.
In the traditional use of the electroslag process, ingots are prepared by remelting an electrode of almost identical composition to that of the required finished product. Usually some purification, such as sulfur reduction, also occurs as the molten metal droplets fall through the slag and non-metallic inclusions are removed or at least redistributed. An extension of the electroslag process was proposed by British Patent No. 1,251,660. This patent discloses use of a hollow, consumable, pipe-like electrode filled with prereduced iron powder, along with alloying constituents if desired, to form a steel ingot of the desired composition. Alternatively, the patent discloses use of a non-consumable, hollow graphite electrode through which iron powder and alloying ingredients are fed. Another reported technique, that of A. G. Thomas, published as "Direct Electroslag Melting of Steel, Refractory Metal and Ferroalloys" Proceedings of the Third International Symposium on Electroslag and Other Special Melting Technology, ASM and Mellon Institute, Part III, 1971, pp. 69-82, utilized a consumable electrode of mild steel. During melting, alloying powders were added to produce steel ingots of the desired composition. Alternatively, a non-consumable graphite or watercooled copper electrode was used to provide the necessary heat. Powdered sponge iron was added during the melt to produce homogenous ingots, either of stainless steel or mild steel. Additionally, partial, preliminary results of our research were presented at the AIME Annual Meeting, Dallas, Texas on Feb. 28, 1974.